1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and more particularly, to a method of driving a PDP of the ac discharge type having a preliminary discharge period for applying a preliminary discharge pulse or pulses to the scan electrodes and/or the sustain electrodes, a scan period for applying successively scan pulses to the individual scan electrodes, and a sustain period for applying sustain pulses to the scan and/or sustain electrodes.
2. Description of the Related Art
PDPs, which display images by utilizing light emission due to gas discharge, have ever been known as a display device that can be easily fabricated to have a large-sized flat screen. PDPs are divided into two types (i.e., the dc type and the ac type) according to the difference in the panel structure and operation principle. The dc-type PDPs have electrodes exposed to the discharge spaces while the ac-type PDPs have electrodes covered with dielectric.
The PDP according to the invention is of the ac-type and thus, only the ac-type PDPs will be explained below.
The ac-type PDPs have a typical configuration as shown in FIGS. 45, 46, and 47. FIG. 45 is a partially cutaway, perspective view showing the main elements or parts of the typical ac-type PDP, FIG. 46 is a cross-sectional view along the line XXXXVIxe2x80x94XXXXVI in FIG. 45, and FIG. 47 is a cross-sectional view along the line XXXXVII-XXXXVXI in FIG. 45.
As seen from FIGS. 45 to 47, the typical ac-type color PDP comprises two opposing dielectric substrates, i.e., a front substrate 51 and a rear substrate 52, that form a gap between them. The substrates 51 and 52 are typically made of glass. The following structure is provided in the gap.
Specifically, on the inner surface of the front substrate 51, scan electrodes 53 and sustain electrodes 54 are formed to be parallel to each other. The scan electrodes 53 and the sustain electrodes 54 constitute row electrodes. The electrodes 53 and 54 are covered with a dielectric layer 55a such as MgO. The dielectric layer 55a is covered with a protection layer 56.
On the inner surface of the rear substrate 52, data electrodes 57 are formed to be parallel to each other. The electrodes 57 are perpendicular to the row electrodes (i.e., the scan and sustain electrodes 53 and 54). The data electrodes 57 are covered with a dielectric layer 55b such as MgO. To convert the ultraviolet (UV) rays emitted by discharge to visible light, a phosphor layer 58 is formed on the layer 55b. The layer 58 includes three types of phosphor sublayers for three primary colors of red (R), green (G), and blue (B) arranged in the respective discharge cells, making it possible to display color images.
Partition walls 60 are provided in the gap between the front and rear substrates 51 and 52 to form the discharge cells, defining discharge spaces 59 for the respective cells. A gaseous mixture of at least two ones of He, Ne, Ar, Kr, Xe, N2, O2 and CO2 is filled in the respective spaces 59 as the discharge gas.
FIG. 48 is a plan view showing the electrode structure of the color PDP shown in FIGS. 45 to 47.
As shown in FIG. 48, the count of the scan electrodes 53 extending along the rows of the PDP is m, where m is a natural number greater than unity. The scan electrodes 53 are referred as Si (i=1, 2, . . . , m). The count of the data electrodes 57 extending along the columns of the PDP is n, where n is a natural number greater than unity. The data electrodes 57 are referred as Dj (j=1, 2, . . . , n). The discharge cells 61 are located at the respective intersections of the scan and data electrodes 53 and 57. Thus, the cells 61 are arranged in a matrix array.
The count of the sustain 54 extending along the rows of the PDP is m. Each of the sustain electrodes 54 and a corresponding, adjoining one of the scan electrodes 53, which are parallel to and apart from each other at a specific interval, forms an electrode pair. The sustain electrodes 54 are referred as Ci (i=1, 2, . . . , m).
With the above-described ac-type color PDP, electric charge caused by discharge in the discharge spaces 59 is temporarily stored in the dielectric layers 55a and/or 55b and is eliminated therefrom. The electric charge (which may be termed simply xe2x80x9cchargexe2x80x9d hereinafter) stored in the layers 55a and 55b is termed the xe2x80x9cwall chargexe2x80x9d. Generation and elimination of the discharge is controlled by adjusting or controlling the amount and/or distribution state of the xe2x80x9cwall chargexe2x80x9d.
Next, an example of the conventional methods of driving the above-described ac-type PDP is explained below with reference to FIGS. 1 and 2.
FIG. 1 shows schematically the waveforms of the driving voltage applied to the respective electrodes. FIGS. 2A to 2F show schematically the distribution of the wall charge in the respective electrodes.
In FIG. 1, the period of time T2 in which the elimination pulse 105 and the preliminary discharge pulses 106 and 107 are applied is termed the xe2x80x9cpreliminary discharge periodxe2x80x9d. The period of time T3 in which the scan pulse 108 and the data pulse 109 are applied is termed the xe2x80x9cscan periodxe2x80x9d. The period of time T4 in which the sustain pulse 110 is applied is termed the xe2x80x9csustain periodxe2x80x9d. The combination of the xe2x80x9cpreliminary discharge period T2xe2x80x9d, the xe2x80x9cscan period T3xe2x80x9d, and the xe2x80x9csustain period T4xe2x80x9d is termed the xe2x80x9csub-field T1xe2x80x9d. In other words, the xe2x80x9csub-field T1xe2x80x9d is formed by the preliminary discharge period T2, the scan period T3, and the sustain period T4.
The sub-field T1 corresponds to each cycle of the conventional driving method of the PDP explained here. Thus, the waveform diagram during one of the sub-fields T1 is shown in FIG. 1 and the change of the wall charge distribution during the same is shown in FIG. 2.
In the subsequent explanation in this specification, the rise of a positive pulse means the positive change of the voltage (i.e., the increase of the absolute value or amplitude of the voltage), and the fall of a positive pulse means the negative change of the voltage (i.e., the decrease of the absolute value or amplitude of the voltage). Also, the rise of a negative pulse means the negative change of the voltage (i.e., the increase of the absolute value or amplitude of the voltage), and the fall of a negative pulse means the negative change of the voltage (i.e., the decrease of the absolute value or amplitude of the voltage).
(1. Elimination of Sustain Discharge)
The rectangular elimination pulse 105 is applied to all the sustain electrodes 54 (C1 to Cm). Thus, the ac discharge occurring in the light-emitting cells 61 due to the application of the rectangular sustain pulses 110 is stopped and at the same time, the wall charge stored in the dielectric layers 55a and 55b decreases or disappear. This operation to apply the elimination pulse 105 is termed the xe2x80x9csustain discharge eliminationxe2x80x9d. FIG. 2A shows the state where the wall charge stored in the dielectric layers 55a and 55b has disappeared.
Several methods for the xe2x80x9csustain discharge eliminationxe2x80x9d have been known. In the method shown in FIG. 1, a narrow rectangular pulse is used as the elimination pulse 105. However, as the elimination pulse 105, a rectangular pulse 105a with a less amplitude and a greater width shown in FIG. 3 than the pulse 105 shown in FIG. 1 may be used. Also, a sawtooth-shaped pulse 105b with a linearly-increasing amplitude shown in FIG. 4 may be used as the elimination pulse 105.
(2. Preliminary Discharge)
After eliminating the sustain discharge by the pulse 105, a preliminary discharge pulse 106 is commonly applied to all the sustain electrodes 54 (C1 to Cm) while a preliminary discharge pulse 107 is commonly applied to all the scan electrodes 53 (S1 to Sm). At the rise time (i.e., at the leading edges) of the pulses 106 and 107, all the cells 61 are compulsively discharged. Thus, as shown in FIG. 2B, negative wall charge is generated and stored at the respective scan electrodes 53 while positive wall charge is generated and stored at the respective sustain electrodes 54. This discharge occurring at the leading edges of the pulses 106 and 107 is termed the xe2x80x9cpreliminary dischargexe2x80x9d.
At the subsequent fall time (i.e., at the trailing edges) of the pulses 106 and 107, discharge takes place in all the cells 61, thereby eliminating the wall charge stored in all the cells 61. The state of the wall charge distribution at this stage is shown in FIG. 2C. This discharge occurring at the fall time of the pulses 106 and 107 is termed the xe2x80x9cpreliminary discharge eliminationxe2x80x9d.
The xe2x80x9cpreliminary dischargexe2x80x9d and the xe2x80x9cpreliminary discharge eliminationxe2x80x9d facilitate the subsequent xe2x80x9cwriting dischargexe2x80x9d.
The xe2x80x9cpreliminary discharge eliminationxe2x80x9d eliminates the wall charge or decreases the wall charge to a level that prevents error discharge from occurring in the scan period T3 and the sustain period T4 prior to the writing discharge. Thus, the writing discharge is facilitated and at the same time, the error discharge due to the remaining wall charge in the unselected cells 61 is prevented in the periods T3 and T4.
In this example, the preliminary discharge is caused by the rise (i.e., the leading edge) of a rectangular pulse (106 or 107) applied commonly to the scan electrode 53 (S1 to Sm) and is eliminated by the fall (i.e., the trailing edge) of the same pulse. However, the preliminary discharge and its elimination maybe caused by separate pulses. For example, as shown in FIG. 5, the preliminary discharge is caused by a positive rectangular pulse 107a applied commonly to the scan electrode 53 (S1 to Sm) and its elimination is caused by a negative rectangular pulse 107b applied commonly to the same.
Moreover, the preliminary discharge pulse is not limited to a rectangular pulse. The preliminary discharge pulse may have any waveform capable of causing the above-described preliminary discharge operation. For example, a sawtooth-shaped pulse 107c with a linearly-increasing amplitude shown in FIG. 6 may be used as the preliminary discharge pulse.
(3. Writing Discharge)
After the preliminary discharge is eliminated, the rectangular scan pulses 108 are successively applied to the scan electrodes 53 (S1 to Sm) at different timing so as to scan them. At the same time as this, the rectangular data pulses 109 according to the image data to be displayed are applied to the data electrodes 57 (D1 to Dn) in synchronization with the scan pulses 108. The cells 61 are turned on or off according to existence or absence of the corresponding data pulses 109. For example, if one of the cells 61 is applied with the data pulse 109 along with the scan pulse 108, discharge occurs in the space 59 of the cell 61 in question. On the other hand, no discharge occurs in the cells 61 applied with no data pulse 109. Thus, the image data to be displayed is written into the selected cells 61 according to the existence and absence of discharge in the spaces 59. This discharge is termed the xe2x80x9cwriting dischargexe2x80x9d.
(4. Sustain Discharge)
In the selected cells 61 where writing discharge has occurred, positive wall charge is stored in the dielectric layer 55a over the scan electrodes 53 and at the same time, negative wall charge is stored in the dielectric layer 55b over the data electrodes 57. As a result, the wall charge distribution in the selected cells 61 has a state shown in FIG. 2D. On the other hand, no writing discharge occurs in the unselected cells 61 and thus, the wall charge distribution is kept in the state shown in FIG. 2C.
In the selected cells 61, thereafter, the positive potential due to the positive wall charge stored in the dielectric layer 55a over the scan electrodes 53 is superposed the inter-electrode voltage between the sustain electrodes 54 and the corresponding scan electrodes 53 due to the first one of the sustain pulses 110, causing the xe2x80x9cfirst sustain dischargexe2x80x9d.
When the first sustain discharge has occurred, the wall charge distribution changes to the state shown in FIG. 2E. Specifically, positive wall charge is stored in the dielectric layer 55a over the sustain electrodes 54 and at the same time, negative wall charge is stored in the same dielectric layer 55a over the scan electrodes 53. Thereafter, the potential difference due to the positive and negative wall charge stored in the dielectric layer 55a is superposed the inter-electrode voltage between the sustain electrodes 54 and the corresponding scan electrodes 53 due to the second one of the sustain pulses 110, causing the xe2x80x9csecond sustain dischargexe2x80x9d.
Because of the xe2x80x9csecond sustain dischargexe2x80x9d, the wall charge distribution changes to the state shown in FIG. 2F, where negative wall charge is stored in the dielectric layer 55a over the sustain electrodes 54 and positive wall charge is stored in the same dielectric layer 55a over the scan electrodes 53.
Thus, the potential difference due to the stored wall charge by the sustain discharge according to the k-th sustain pulse 110 is superposed the inter-electrode voltage between the sustain electrodes 54 and the corresponding scan electrodes 53 due to the (k+1)-th sustain pulse 110, causing the xe2x80x9c(k+1)-th sustain dischargexe2x80x9d. As a result, the sustain discharge is continued.
Normally, the voltage value (i.e., amplitude) of the sustain pulses 110 is determined or adjusted in advance in such a way that the application of the pulse 110 alone without the inter-electrode voltage is unable to cause any discharge. Therefore, sustain discharge occurs in the cells 61 where writing discharge has occurred while sustain discharge does not occur in the cells 61 where writing discharge has not occurred.
Next, a method of displaying images with gradation is explained below with reference to FIG. 49.
A field T0 (e.g., {fraction (1/60)} second), which is a period of time for displaying an image, is divided into several sub-fields. In the example in FIG. 49, the field T0 is divided into four sub-fields T1-1, T1-2, T1-3, and T1-4. Each of the sub-fields T1-1, T1-2, T1-3, and T1-4 has the configuration shown in FIG. 1; i.e., each sub-field T1-1, T1-2, T1-3, or T1-4 comprises the preliminary discharge period T2, the scan period T3, and the sustain period T4. In each sub-field T1-1, T1-2, T1-3, or T1-4, the operation to display or not to display an image is adjustable independently. Also, the count of the sustain pulses 110 included in each sub-field T1-1, T1-2, T1-3, or T1-4 is different from each other and thus, it provides different brightness levels.
In the field T0 comprising the four sub-fields T1-1, T1-2, T1-3, and T1-4, for example, the individual sub-fields T1-1, T1-2, T1-3, and T1-4 are designed to provide different brightness levels having a ratio of 1:2:4:8. In this case, due to selection and combination of the sub-fields T1-1, T1-2, T1-3, and T1-4 that provide different brightness levels, images can be displayed at 16 brightness levels. When none of the sub-fields is selected, the brightness level is set as 0. The brightness level is set as 15 when all the sub-fields is selected.
With the above-described conventional ac-type PDP, the voltage applied across the scan electrodes 53 and the data electrodes 57 at the writing discharge (which may be termed the xe2x80x9cwriting voltagexe2x80x9d hereinafter) has a narrow permissible range that provides normal and desired operation of the PDP. Thus, if the permissible range of the writing voltage in the respective cells 61 fluctuates due to parameter variation in the fabrication process sequence of the PDP, there arises a problem that a part of the cells 61 emit light in error and another part of the cells 61 emit no light in error. This means that the PDP does not display correct images as desired.
Therefore, there has been the strong need to develop the technique that makes it possible to cause desired writing discharge even if the writing voltage is lowered.
The above need may be solved by the method to use the superposed wall discharge stored in the dielectric layer over the scan electrodes or the data electrodes. In this case, however, the storing behavior of the wall charge in the dielectric layer over the scan or data electrodes is difficult to be controlled. Thus, there arises a problem that too much wall discharge is stored, thereby causing error discharge. Alternately, there arises a problem that too little wall discharge is stored and thus, a desired writing voltage is unable to be generated.
Accordingly, an object of the present invention to provide a method of driving an ac-discharge type PDP that expands the permissible range of the voltage applied across the scan and data electrodes at writing discharge.
Another object of the present invention to provide a method of driving an ac-discharge type PDP that ensures desired writing discharge generation even if the writing voltage has a comparatively small amplitude.
Still another object of the present invention to provide a method of driving an ac-discharge type PDP that displays desired images correctly at high quality even if the writing voltage has a comparatively small amplitude.
A further object of the present invention to provide a method of driving an ac-discharge type PDP that prevents error discharge.
A still further object of the present invention to provide a method of driving an ac-discharge type PDP that controls easily and correctly the storing behavior of the wall charge in the dielectric layer over the scan or data electrodes.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to the present invention, a method of driving an ac-discharge PDP is provided. The PDP comprises scan electrodes and sustain electrodes extending in parallel in a first direction and data electrodes extending in a second direction. The scan electrodes, the sustain electrodes, and the data electrodes form cells arranged regularly for displaying images using discharge-induced emission.
The method comprises:
(a) a wall-charge adjustment step of storing first wall-charge of a first polarity near the respective scan electrodes and second wall-charge of a second polarity near the respective sustain electrodes, where the second polarity is opposite to the first polarity;
the first wall-charge of the first polarity stored near the respective scan electrodes generating an associate electric-field in the cells;
the wall-charge adjustment step being performed by (i) applying commonly a first wall-charge adjustment voltage pulse to the scan electrodes, or (ii) applying commonly a second wall-charge adjustment voltage pulse to the sustain electrodes, or (iii) applying commonly a first wall-charge adjustment voltage pulse to the scan electrodes and applying commonly a second wall-charge adjustment voltage pulse to the sustain electrodes; and
(b) a writing discharge generating step of generating writing discharge in the desired cells;
the writing discharge generation step being performed after the wall-charge adjustment step by applying successively a scan voltage pulse to the scan electrodes and applying a data voltage pulse to the data electrodes according to desired image data;
the scan voltage pulse and the data voltage pulse generating a main electric-field in the cells;
the main electric-field cooperating with the associate electric-field, thereby generating a writing voltage in the cells.
With the method according to the first aspect of the present invention, prior to the writing discharge generation step of generating the writing discharge in the desired cells, the wall-charge adjustment step of storing the first wall-charge of the first polarity near the respective scan electrodes and the second wall-charge of the second polarity near the respective sustain electrodes is performed. Thus, before the writing discharge generation step begins, the first wall-charge is stored near the respective scan electrodes and the second wall-charge is stored near the respective sustain electrodes, generating the associate electric-field in the cells.
On the other hand, in the writing discharge generation step, the scan voltage pulse is successively applied to the scan electrodes and the data voltage pulse is applied to the data electrodes according to the desired image data, generating the main electric-field in the cells. The main electric-field cooperates with the associate electric-field, thereby generating the writing voltage in the cells.
As a result, the writing discharge is generated or caused by the sum of the main electric-field and the associate electric-field, which ensures desired writing discharge generation even if the writing voltage has a comparatively small amplitude. In other words, the permissible range of the voltage applied across the scan and data electrodes at the writing discharge is expanded. Consequently, desired images are displayed correctly (without any error discharge) at high quality even if the writing voltage has a comparatively small amplitude.
Moreover, the wall-charge adjustment step is performed by application of at least one of the first and second wall-charge adjustment voltage pulses and therefore, the amount of the first wall charge and that of the second wall charge can be well adjusted or controlled by changing/adjusting the waveform, amplitude, width, and/or polarity of the at least one of the first and second wall-charge adjustment voltage pulses. This means that the desired writing discharge is caused more easily compared with the case where the wall-charge adjustment step is not included.
In a preferred embodiment of the method according to the invention, at least one of the first and second wall-charge adjustment voltage pulses is prepared independent of a preliminary discharge pulse for generating preliminary discharge. The at least one of the first and second wall-charge adjustment voltage pulses is applied after the preliminary discharge pulse is applied.
In another preferred embodiment of the method according to the invention, at least one of the first and second wall-charge adjustment voltage pulses is prepared to be combined with a preliminary discharge pulse for generating preliminary discharge. The at least one of the first and second wall-charge adjustment voltage pulses is applied after the preliminary discharge pulse is applied.
It is preferred that at least one of the first and second wall-charge adjustment voltage pulses has a part whose amplitude varies. More preferably, the at least one of the first and second wall-charge adjustment voltage pulses has a part whose amplitude varies approximately linearly.
In still another preferred embodiment of the method according to the invention, an associate scan voltage pulse is commonly applied to the sustain electrodes in the writing discharge generation step. The associate scan voltage pulse serves to decrease or eliminate the second wall-charge stored near the respective sustain electrodes in the cells, preventing error discharge.
In a further preferred embodiment of the method according to the invention, a wall-charge elimination voltage pulse is commonly applied to the scan electrodes after the writing discharge generation step is finished. The wall-charge elimination voltage pulse serves to decrease or eliminate the first and second wall-charge left near the respective scan and sustain electrodes in the cells where no writing discharge has occurred, preventing light from being emitted in error.